The present invention relates to an electron-beam image transfer device for transferring a pattern on a photoelectric mask onto a specimen such as a semiconductor wafer.
With the recent increase in the integrated circuit density, photolithography which had so far constituted the mainstream of the micropattern forming technology came to be found to have its limitations and a rapid progress has been made in a new lithographic method using electron-beams and X-rays to overcome such limitations. As a result there has recently invented an electron-beam image transfer device in which a photoelectric mask which is disposed parallel to a specimen is irradiated with ultraviolet rays and the photoelectrons which are liberated as a result are focused on the specimen by means of the uniform electric field and magnetic field between the specimen and the mask so that the whole pattern can be transferred from the mask to the specimen. This device has practical advantage in that it offers high productivity because it is capable of high-speed image transfer and that it permits the use of the conventional techniques because the photoelectric mask used is similar in construction to the photomask and that it enables the transfer of an image onto an irregular surface because of a deep depth of focus. For these reasons, this device is highly promissing for use in the processing of submicron patterns. The effectiveness of equipment like this is mentioned in literature such as R. Ward, J. Vac. Sci. Technology, 1b(b), Nov/Dec, 1979.
FIG. 1 is a schematic diagram showing an exemplary electron-beam image transfer device. In FIG. 1, numeral 1 shows a vacuum vessel which constitutes the image transfer chamber. This vessel 1 is evacuated to somewhere around 10.sup.-6 Torr by means of a vacuum pump. In the evacuated vessel 1 are disposed a specimen holding means 4 for holding a specimen 3 and a photoelectric mask holding means 6 for holding a photoelectric mask 5. The specimen 3 and the photoelectric mask 5 are spaced about 10 mm apart in facing relation to each other. As seen from the enlarged view shown in FIG. 2, said photoelectric mask is formed by a quartz plate 5a which passes ultraviolet rays, a master pattern 5b which consists of ultraviolet ray absorbing material forming the desired pattern on the quartz plate, and a photoelectric surface 5c made of CsI which emits photoelectrons when it receives the ultraviolet rays coming through the master pattern 5b. The surface of said specimen 3 which faces the photoelectric mask 5 is coated with electron-beam sensitive resist 3a. A detector 7 detects the relative position of the specimen 3 and the photoelectric mask so that they may be properly positioned by thus obtained information.
The light source 8 is provided outside said evacuated vessel 1. The light source 8 emits ultraviolet rays which are caused to strike said photoelectric mask 5 through an ultraviolet ray passing window 10 when a shutter 9 is opened. Outside the evacuated vessel 1 are also provided Helmholtz coils 11 and a DC power source 12. A magnetic field is produced along the direction in which said specimen 3 and mask 5 are placed by means of said coil 11 and an electric field is produced in the same direction by means of said power source 12. The numerals 13, 14, 15 in FIG. 1 indicate a support plate, shock-absorbing rubber, and mount, respectively.
When the ultraviolet rays from said light source 8 are incident on the photoelectric mask 5, said mask 5 emits photoelectrons according to the mask pattern 5b and thus liberated photoelectrons are focused by said magnetic and electric fields and projected onto the specimen 3. As a result the resist 3a of the specimen 3 is exposed according to said master pattern 5b. Thus the whole image of the master pattern 5b can be transferred to the specimen 3 to provide the previously mentioned advantage.
However, this type of equipment was associated with the following problems. When the transfer of a pattern is completed, it is necessary to change the specimen 3. Since the vacuum vessel is opened to the atmosphere each time the specimen 3 is changed, the photoelectric mask 5 undergoes serious deterioration by absorbing moisture. It is also necessary to evaporate a coating of CsI on the surface of the photoelectric mask 5 each time about 50 patterns have been transferred, thus so much lowering productivity. Furthermore the specimen table 2 or the mask table 4 must be removed out of the image transfer chamber 1 when the specimen 3 or the photoelectric mask 5 is changed and as a result the image transfer accuracy is reduced by the effects of dust and temperature changes.